1. Field of the Invention
The present invention relates generally to a container end closure system and more particularly to closure ends, to containers made using these container ends, and to processes of making containers.
2. Prior Art
Although there are many types of containers in which consumer goods are packaged and sold, one popular type incorporates a cylindrical or rectilinear tube formed largely of fibrous material such as paper. Many containers of this type are interiorly coated or lined with metal or plastic in order to accomodate products which are incompatible with the fibrous material which provides the majority of the strength and substance of the container walls.
A wide variety of consumer goods are packaged and sold in containers of this type. Examples include liquids such as motor oils, particulate products, such as household cleansers, powdered bleach, hot chocolate mix, popcorn and the like, and articles such as potato chips, pastry products, and ready-to-use frostings. It will accordingly be apparent that fiber tube containers are ubiquitous in the market place and that considerable effort has previously been expended in attempts to provide fiber tube containers of high quality at the least possible cost.
In the manufacture of the fiber tube portions of containers of this type, two types of construction are presently in wide use. One type is made of a helically wound paper strip which forms a cylindrical tube. The other type employs a paper strip wound perpendicularly to the axis of the tube, and this type of construction is utilized to form containers of either cylindrical or rectilinear shape. In both construction techniques, once a substantial length of wound container tube stock has been fabricated, it is cut to form container tubes of desired lengths, and labels are applied. An end closure is applied to one end of each labeled container tube, and the partially completed container is filled with a product before the other end is sealed with another end closure.
Typically, although not necessarily, one of the end closures incorporates an opening, a spout or an openable cover to facilitate removing contents from the container. The technique for removing container contents varies as widely as the nature of products packaged in fiber tube containers. Many containers incorporate a tear strip approach which partially or wholly destroys the top closure. Others employ a removeable or resealable member for providing an opening in the top end closure, while still others use a wall-mounted pour spout or provide some manner of breaking away a portion of the tube wall.
Common to the manufacture of fiber tube containers of any description is the problem of applying end closures at high speeds and in such a manner that (1) will assure the retention of the closure on the tube and (2) will consistently provide an air-tight seal between the closure and the tube. Present day end closures for fiber tube containers are almost universally formed from metal. Each metal end closure has a circumferentially extending rim of generally U-shape cross-section to receive end wall portions of a fiber tube. The metal rim is crimped, rolled or otherwise cold worked to captivate the fiber tube end in the bight of the rim.
The use of metal end closures is replete with disadvantages. To begin with, any suitable metal material is expensive. In order to satisfy the need for a pleasing external appearance and the requirement for an interior that does not corrode or otherwise deleteriously affect container contents, the metals employed in end closures for consumer quality containers are particularly expensive. Obtaining an air-tight seal between a fiber tube end and a metal closure is a difficult requirement to fulfill in a high-speed packaging system. Moreover, available present-day equipment for attaching metal end closures to fiber tubes is neither small, nor light, nor inexpensive, nor of suitably high speed, despite its long history of development and refinement that has gone into this equipment.
In view of the many drawbacks encountered with the use of metal end closures on fiber tube containers, it is not surprising that a number of attempts have been made to use end closures formed from plastics materials. Plastics are preferable to metal for several reasons. Exteriorly, plastics closures can be as inconspicuous or as attractive as marketing techniques dictate. Interiorly, plastics are desirably unreactive and neither corrode in response to contact with nor promote deterioration of many products. Moreover, there is no difficulty in forming or shaping most plastics materials into the desired closure shapes due to the advanced state of injection molding and die stamping techniques.
The principal problem encountered in using plastics materials for container end closures lies in attaching formed plastics closures to tube ends in a quick, reliable and inexpensive manner which consistently produces air-tight seals. Container closure attachment speeds of 3 to 20 or more containers per second are needed to achieve compatability with existing packaging equipment, and prior proposals have not met these needs.
One proposal for securing plastics closures to fiber tubes is analogous to techniques used with metal closures. A plastics closure is provided with a rim of generally U-shape cross-section into which the fiber tube end region is inserted. The rim has leg portions which are rolled or crimped in an attempt to captivate the tube end region. This proposal has uniformly met with failure because plastics materials, as the name "plastics" implies, do not typically have a precise or predetermined elastic limit and accordingly tend to return to their original shape unless stressed quite severely or treated in some other way to relieve their "memory" of a prior shape. Consequently, plastics closures applied in this fashion either do not consistently remain affixed to the tube end and/or do not consistently maintain an air-tight seal.
In order to overcome these difficulties, attempts have been made to indent a portion of the U-shape rim of plastic closures in order to stress the material so severely as to prevent memory rebound. This approach has been somewhat more successful in retaining plastics closures on the tube end but has not been successful in consistently providing an air-tight seal between the plastic closure and the tube end.
Other attempts to affix plastics closures on tube ends have involved heating or otherwise welding plastics closures to the tube ends. Welding techniques are described, for example, in U.S. Pat. Nos. 2,795,348; 3,475,243; and 3,578,524, while induction heating techniques, such as corona discharge, as described in U.S. Pat. No. Re 26,110, and ultrasonic bonding, as shown in U.S. Pat. No. 3,824,138, have also been attempted. While these approaches may be operable from a technical standpoint, plastics closures affixed in any of these fashions are not in widespread commercial use due to the high cost of equipment and their low rates of production.
It would appear, at first blush, that adhesively attaching a plastic closure to a tube end would be a fruitful approach. One difficulty with this approach resides in designing a technique to attach closures at a high speed (for example, in the range of 3 to 20 or more per second) without requiring a multiplicity of work stations and while allowing each container to be filled within a few seconds after its first end closure is attached. Conceivably, production rates of this magnitude could be achieved using very quick setting adhesives; but any adhesive which sets up rapidly enough to allow such a production rate would surely set up in the discharge end of the adhesive dispenser each time production is interupted, however momentarily. Recognizing these drawbacks, proposals have been made to utilize slower-acting adhesives and to hasten their bonding by the application of heat, as described in U.S. Pat. No. 2,413,449, or by the application of laser energy, as described in U.S. Pat. No. 3,960,624.
Perhaps the approach in the prior art closest to the system of the present invention is found in U.S. Pat. No. 2,802,593 where it is stated that a flange carries an internal bead in contact with the container to provide a capillary space into which solvent or adhesive can be positioned by capillary action. One difficulty with this approach lies in the positioning of the bead near the peripheral flange edge which limits the area of extent of the adhesive bond. Another difficulty with this approach lies in the creation of an annular bead on the inside of a leg of a peripherally extending U-shape rim. Since the legs of the rim are quite closely spaced, it is virtually impossible to withdraw the mold from a U-shape rim while forming a radially extending bead.